Radiation-emitting semiconductor chip

ABSTRACT

A radiation-emitting semiconductor chip is specified, comprising a semiconductor body ( 3 ) having an n-conducting region ( 4 ) and a p-conducting region ( 5 ), the semiconductor body having a hole barrier layer containing a material from the material system In y Ga 1-x-y Al x N.

RELATED APPLICATIONS

This patent application claims the priority of German patentapplications 10 2005 035 721.0 filed Jul. 29, 2005 and 10 2005 048 196.5filed Oct. 7, 2005, the disclosure content of which is herebyincorporated by reference

FIELD OF THE INVENTION

The present invention relates to a radiation-emitting semiconductor chiphaving an active region suitable for generating radiation.

BACKGROUND OF THE INVENTION

The internal quantum efficiency of semiconductor chips when generatingradiation, in particular those which are based on nitride compoundsemiconductor materials, often depends crucially on the operatingcurrent density with which the semiconductor chip is operated. Here, theexpression “internal quantum efficiency” is understood to mean the ratioof the number of charge carriers of one type—electrons or holes—that areinjected into the active region to the number of photons generatedtherefrom in the active region.

The greater the operating current density, particularly in the case ofnitride-based semiconductor chips, the lower is the internal quantumefficiency. More efficient operation of semiconductor chips at highcurrent densities would make it easier to generate an increasedradiation power cost-effectively, without enlarging the active area,i.e. the area of the active region of the chip, with this semiconductorchip.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductor chipwhich can be formed in a simplified manner with a reduced dependence ofthe internal quantum efficiency on the operating current density.

This and other objects are attained in accordance with one aspect of thepresent invention directed to a radiation-emitting semiconductor chipthat comprises a semiconductor body, which has an n-conducting regionand a p-conducting region, an active region suitable for generatingradiation being arranged between the n-conducting region and thep-conducting region, in which active region electrons passed into theactive region via the n-conducting region and holes passed into theactive region via the p-conducting region recombine with generation ofradiation. A hole barrier layer is arranged on an opposite side of theactive region of the semiconductor chip from the p-conducting region,said hole barrier layer containing a material from the III-Vsemiconductor material system In_(y)Ga_(1-x-y)Al_(x)N where 0≦x≦1,0≦y≦1, and x+y≦1, the hole barrier layer being transmissive forelectrons.

The hole barrier layer is preferably arranged in the semiconductor bodyand formed in such a way that it reduces or completely blockspenetration of holes into the n-conducting region.

The hole barrier layer thus impedes the penetration of holes to then-conducting region and thus reduces the probability of holesrecombining with electrons non-radiatively in the n-conducting region.The probability of holes recombining radiatively in the active region iscorrespondingly increased since, by means of the hole barrier layer, theholes are kept to an increased extent on that side of the hole barrierlayer which faces the active region. In particular, even for highcurrent densities holes can in this way be kept to an increased extenton that side of the hole barrier layer which faces the active region.The internal quantum efficiency can accordingly be advantageouslyincreased by means of the hole barrier layer. The dependence of theinternal quantum efficiency on the operating current density isadvantageously reduced by means of the hole barrier layer. This ismanifested to a particular degree at comparatively high currentdensities since the probability of holes entering in the n-conductingregions generally increases greatly and nonlinearly as the operatingcurrent density increases.

The hole barrier layer is preferably formed in such a way that theprobability of passage of electrons through the hole barrier layer isgreater than the probability of passage of the holes through the holebarrier layer. For this purpose, a barrier for the passage of electronsthrough the hole barrier layer is preferably smaller than a barrier forthe passage of holes through the hole barrier layer.

This may be achieved by forming the hole barrier layer in a suitablemanner. By way of example a potential barrier for the hole is formed bymeans of the hole barrier layer. The higher the said potential barrier,the lower generally is the probability of passage of the holes.Furthermore, the probability of passage generally also decreases as thethickness of the hole barrier layer increases. The potential barrier maybe set by means of a band gap of the hole barrier layer. If appropriatethe potential barrier for the holes may be increased by suitable dopingin particular by suitable n-conducting doping, particularly preferablythe potential barrier for electrons being simultaneously reduced.

The ratio of the probability of passage of the holes through the holebarrier layer to that of the electrons may be for example 1/10 or less,preferably 1/100 or less, particularly preferably 1/1000 or less. Thesmaller said ratio, the lower the risk of the hole barrier layerreducing, by a blockage of the electrons, the internal quantumefficiency on account of the then reduced number of electrons reachingthe active region.

The hole barrier layer is preferably arranged between the n-conductingregion and the active region. The penetration of holes into then-conducting region can be reduced particularly effectively by means ofsuch an arrangement. The hole barrier layer may be embodied in intrinsicfashion, i.e., in undoped fashion. A undoped layer can be fabricated ina simplified manner, if appropriate, relative to a doped layer. As analternative, however, the hole barrier layer may also be embodied indoped fashion, in particular doped in n-conducting fashion. The holebarrier layer is then expediently integrated in the n-conducting region.

An arrangement of the hole barrier layer on a side of the n-conductingregion that faces the active region in the n-conducting region isfurthermore particularly expedient for a hole barrier. The n-conductingregion is preferably delimited by the hole barrier layer on the part ofthe active region.

Furthermore, the hole barrier layer preferably adjoins the active regionor the hole barrier layer delimits the active region. In the lattercase, the hole barrier layer may for example simultaneously serve as aconfinement layer for the active region, by means of which chargecarriers can be confined in the active region. An arrangement of thehole barrier layer as close as possible to the active region isparticularly advantageous for a hole barrier layer.

In one preferred configuration, the aluminum content x in the holebarrier layer is greater than 0. The band gap of the hole barrier layercan be set by means of the aluminum content and the height of theresulting potential barrier for the holes can be determined in this way.The greater the aluminum content the larger generally is the band gap ofthe hole barrier layer. The barrier height generally also increases withthe band gap.

The aluminum content x is preferably greater than or equal to 0.2,particularly preferably greater than or equal to 0.5, for example upto 1. Aluminum contents of this type make it possible to achieve anefficient hole blockade by means of the hole barrier layer, inparticular in a semiconductor body based on nitride compoundsemiconductors.

As the aluminum content increases, however, generally the latticeconstant of the hole barrier layer also decreases. This holds true inparticular for an indium-free hole barrier layer where y=0. This mayresult in tensile strain in the semiconductor body. Such strain in thesemiconductor body, in particular in the active region, may in turn leadto a reduction of the internal quantum efficiency of the semiconductorchip. This holds true in particular for an active region which containsa layer made from the III-V semiconductor material systemIn_(y)Ga_(1-y)N where 0<y≦1 or is based on said material system. A layermade from said material system is free of aluminum. The lattice mismatchof such a layer with respect to an aluminum-containing layer maytherefore lead to an increased extent to strain in the semiconductorbody, in particular in the active region. In order to keep the strain inthe semiconductor body resulting from the hole barrier layer tolerablysmall, x is preferably less than or equal to 0.45. This is of particularimportance if the hole barrier layer is formed in a manner free ofindium where y=0.

If the hole barrier layer is formed such that it contains indium, i.e.where y is greater than 0, then the lattice constant and the band gap ofthe hole barrier layer can advantageously be set essentiallyindependently of one another by variation of the indium content y andthe aluminum content x.

The hole barrier layer may thus be formed as a buffer layer. By means ofthe buffer layer, it is possible during the production of thesemiconductor body, for example by means of epitaxial growth, tooptimize the lattice constant for further semiconductor layers to beapplied to the buffer layer. Strains can thus be reduced. The holebarrier layer is preferably formed as a buffer layer for the layer(s)for the active region. A reduction of the efficiency of the activeregion, in particular of an InGaN-based active region, can thus beprevented. Here, it is preferred that 0<y<x, in particular 0<y<x≦1. Thetensile strain that occurs in a simplified fashion on account of thecomparatively high aluminum content x can advantageously already besufficiently counteracted by an indium content y smaller than thealuminum content x. The strain is preferably completely avoided.However, an indium-free hole barrier layer containing aluminum can beproduced in simplified fashion relative to a hole barrier layercontaining indium and aluminum.

In a further preferred configuration, the hole barrier layer is embodiedas a tunnel barrier layer, the tunnel barrier layer being formed in sucha way that electrons tunnel through it with a higher probability thanholes. By means of the tunnel barrier layer, a potential barrier isformed both for the electrons and for holes, the respective potentialbarrier having to be overcome by electrons before penetrating into theactive region and by holes before penetrating into the n-conductingregion.

The energy of the conduction band edge of the tunnel barrier layer ispreferably greater than the energy of the conduction band edge of alayer that adjoins the tunnel barrier layer on the part of then-conducting region. The difference between these energies determinesthe maximum barrier height of the potential barrier that is to beovercome by the electrons before penetrating into the active region.

The energy of the valence band edge of the tunnel barrier layer ispreferably less than the energy of the valence band edge of a layerwhich is arranged on a side of the tunnel barrier layer which isopposite to the n-conducting region and, in particular, adjoins thetunnel barrier layer, for example a layer of the active region. Thedifference between these energies determines the maximum barrier heightof the potential barrier that is to be overcome by the holes beforepenetrating into the n-conducting region.

A band gap of the tunnel barrier layer is furthermore preferably largerthan the band gap of a layer that adjoins the tunnel barrier layer onthe part of the n-conducting region and/or a layer that adjoins thetunnel barrier layer on the side which is opposite to the n-conductingregion in the semiconductor body. This facilitates the formation of abarrier for electrons and holes.

The tunneling probability depends on the barrier height and on thebarrier thickness. The thicker the tunnel barrier layer or the higherthe potential barrier, the lower generally is the tunneling probability.The tunneling probability is furthermore determined by the effectivemass of the charge carriers, the tunneling probability generallydecreasing as the effective mass increases. Since the holes regularlyhave an effective mass greater than that of the electrons the tunnelingprobability of the holes is often lower than that of the electrons.

The tunnel barrier layer preferably has a thickness of 8 nm or less,particularly preferably of 4 nm or less. Furthermore, it is preferablythe case that 0.2×0.45. By means of such tunnel barrier layers, it ispossible to form a tunnel barrier which efficiently reduces penetrationof holes into the n-conducting region and only moderately impedes thepassage of electrons from the n-conducting region into the activeregion. Furthermore, strain in the semiconductor body can be keptcomparatively low by choosing the aluminum content in the rangementioned above. The aluminum content for a tunnel barrier layer isparticularly preferably greater than or equal to 0.3.

The tunnel barrier layer may be doped in n-conducting fashion or beembodied in intrinsic fashion. The barrier height for electrons can belowered by n-conducting doping, for example by means of Si. On accountof the band gap that essentially remains constant in the case of thedoping, the barrier for the holes is simultaneously increased by thismeans. An undoped layer can be produced in a simplified manner relativeto a doped layer. Furthermore, it is possible to incorporate defectsinto the tunnel barrier layer, which assist the tunneling of theelectrons and increase the tunneling probability of the electronsrelative to that of the holes. By way of example, Si is suitable as adefect atom.

In a further preferred configuration, the hole barrier layer is formedas a pure hole barrier layer which blocks, in particular completely,holes from passing through. Preferably, the pure hole barrier layer isessentially completely transmissive for the electrons. The pure holebarrier layer furthermore preferably forms a potential barrier for theholes, while in contrast to a tunnel barrier layer the electrons passthrough the pure hole barrier layer essentially in a manner free of apotential barrier. On account of the unimpeded passage of the electronsthrough the pure hole barrier layer, the internal quantum efficiency ofthe semiconductor chip can be increased compared with a tunnel barrierlayer.

Preferably, the pure hole barrier layer is doped in n-conducting fashionin such a way that the energy of the conduction band edge of the holebarrier layer is less than or equal to the energy of the conduction bandedge of a layer adjoining the pure hole barrier layer on the side of thepure hole barrier layer which is opposite to the active region. By wayof example, Si is suitable as donor.

The pure hole barrier layer may have, in particular, such a highpotential barrier and/or thickness that if an electron barrier were alsoformed by means of the hole barrier layer, electrons would not penetratethrough said barrier or would penetrate through it only with theprobability of 10⁻⁵ or less. For a completely transmissive layer, thepassage probability would be equal to 1.

The pure hole barrier layer preferably has a thickness of 11 nm or more.Furthermore, the pure hole barrier layer preferably has a thickness of30 nm or less. A pure hole barrier layer having a thickness of this typehas proved to be particularly suitable for efficiently blockading thepenetration of the holes into the n-conducting region. The hole barrierlayer may, of course, also be embodied with a thickness of more than 30nm, the barrier effect not being considerably intensified by increasingsaid thickness.

Furthermore, an aluminum content 0.2≦x≦0.3 has proved to be particularlyexpedient for a pure hole barrier layer.

In a further preferred configuration, the semiconductor body is arrangedon a carrier. The semiconductor chip then comprises the carrier with thesemiconductor body arranged thereon. The carrier can mechanicallystabilize the semiconductor body, which preferably has a semiconductorlayer sequence having a plurality of semiconductor layers.

By way of example, the carrier may be formed from an epitaxial substrateon which the semiconductor body is grown epitaxially. However, thecarrier may also be different from the epitaxial substrate. If thecarrier is different from the epitaxial substrate, then thesemiconductor chip is also referred to as a thin-film chip. Forthin-film chips, the semiconductor body is preferably firstly grown onthe epitaxial substrate. Afterward, the semiconductor body, preferablyon the side remote from the epitaxial substrate, is arranged andpreferably fixed on the carrier. The epitaxial substrate is thereuponremoved, for example by etching or a laser separating method. Mechanicalsupport of the semiconductor body is ensured by the carrier.

In the case of thin-film chips, the hole barrier layer is preferablyarranged on the side of the active region which is opposite to thecarrier while the hole barrier layer, in the case of non-thin-filmchips, is preferably arranged between the active region and the carrier.Such an arrangement is produced in particular when first then-conducting region of the semiconductor body is grown on the epitaxialsubstrate. The p-conducting region is then arranged on that side of theactive region which is remote from the epitaxial substrate, and isaccordingly arranged on the side of the carrier during the formation ofa thin-film chip, so that the active region is arranged between the holebarrier layer and the carrier.

For thin-film chips, the carrier may be chosen comparatively freely whencompared to an epitaxial substrate, since the requirements made of acarrier for a thin-film chip are generally less stringent than those towhich an epitaxial substrate is subject, for instance with regard to thecrystal structure thereof. The carrier may be chosen for example withregard to optimized thermal and/or electrical conductivity.

A thin-film chip, in particular a thin-film light-emitting diode chip,may furthermore be distinguished by at least one of the followingcharacteristic features:

a reflective layer is applied or formed at a main area—facing thecarrier—of the semiconductor body, which preferably has an epitaxiallayer sequence, said reflective layer reflecting at least part of theelectromagnetic radiation generated in the semiconductor body back intothe latter,

the semiconductor body, in particular the epitaxial layer sequence, hasa thickness in the region of 20 μm or less, in particular in the regionof 10 μm, and/or

the semiconductor body, in particular the epitaxial layer sequencecontains at least one semiconductor layer with at least one area whichhas an intermixing structure which ideally leads to an approximatelyergodic distribution of the light in the semiconductor body, inparticular in the epitaxial layer sequence, i.e. the intermixingstructure has an as far as possible ergodically stochastic scatteringbehavior.

A basic principle of a thin-film light-emitting diode chip is describedfor example in I. Schnitzer et al., Appl. Phys. Lett. 63 (16), Oct. 18,1993, 2174-2176, the disclosure content of which is in this respecthereby incorporated by reference.

A mirror layer is preferably arranged between the carrier and the activeregion, particularly preferably between the semiconductor body and thecarrier. The mirror layer can reflect radiation generated in the activeregion and thus reduce an absorption of radiation in structures, such asthe carrier, for instance, arranged on the side of the mirror layerwhich is opposite to the active region. The mirror layer is particularlypreferably embodied as a metallic mirror layer. A metal-containingmirror layer is distinguished by a reflectivity that generally has anadvantageously low directional dependence. Furthermore, the mirror layeris preferably embodied in electrically conductive fashion and isparticularly preferably electrically conductively connected to theactive region. Electrical contact can thus be made with the chip via themirror layer and, if appropriate, via an electrically conductivecarrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional view of a first exemplary embodimentof a radiation-emitting semiconductor chip according to the invention;

FIG. 2 schematically shows the profile of the valence and conductionband edge for a tunnel barrier layer;

FIG. 3 shows a diagram depicting the tunneling probabilities forelectrons and holes;

FIG. 4 shows results of a simulation calculation for the profile of theconduction and valence band edge for differently formed hole barrierlayers;

FIG. 5 schematically shows the profile of the valence and conductionband edge for a pure hole barrier layer;

FIG. 6 shows a diagram depicting the dependence of the internal quantumefficiency of the semiconductor chip on the operating current densityfor a semiconductor chip with a hole barrier layer and a semiconductorchip without a hole barrier layer; and

FIG. 7 shows a schematic sectional view of a second exemplary embodimentof a radiation-emitting semiconductor chip according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Identical elements, elements of identical type and identically actingelements are provided with identical reference symbols in the Figures.

FIG. 1 shows a schematic sectional view of a first exemplary embodimentof a radiation-emitting semiconductor chip according to the invention.

The semiconductor chip 1 which is preferably embodied as an LED chip,comprises a semiconductor body 3 arranged on a carrier 2. Thesemiconductor body has an n-conducting region 4 and a p-conductingregion 5, between which is arranged an active region 6 suitable forgenerating radiation. The n-conducting and/or the p-conducting regionmay have a plurality of semiconductor layers (not illustrated). A holebarrier layer 7 is formed between the n-conducting region 4 and theactive region 6 or in a manner integrated in the n-conducting region.The hole barrier layer 7 preferably adjoins the active region 6 ordelimits the latter. The hole barrier layer 7 is based on a nitridecompound semiconductor material from the material systemIn_(y)Ga_(1-x-y)Al_(x)N where 0≦x≦1, 0≦y≦1, and x+y≦1 and is formed insuch a way that it reduces or completely blocks penetration of the holesthat are passed into the active zone via the p-conducting region 5during operation of the semiconductor chip 1. The hole barrier layer 7is embodied such that it is transmissive for electrons that are passedto the active region 6 via the n-conducting region 4. Electron-holepairs can recombine in the active region with generation of radiation.

The semiconductor body 3 is preferably grown epitaxially on an epitaxialsubstrate. The carrier 2 may, in particular, be derived from theepitaxial substrate on which a semiconductor layer sequence for thesemiconductor body is grown. For example, the carrier may be a smallpiece of the expitaxial substrate formed from the large area of thesubstrate during singulation of individual chips out of the wafer. Thesemiconductor body is furthermore preferably based on nitride compoundsemiconductor materials. An SiC substrate or a sapphire substrate isparticularly suitable as an epitaxial substrate in this case.

The semiconductor chip is preferably formed for generating ultravioletor visible radiation, in particular from the blue to the green spectralrange. Nitride compound semiconductors are particularly suitable forgenerating radiation in the aforementioned spectral ranges.

The active region 6 is expediently formed in such a way that barriersare formed on both sides around the active region 6 both for theelectrons in the conduction band and for the holes in the valence bandand confine charge carriers in the active region. The internal quantumefficiency of the semiconductor chip can be increased in this way. Oneof said barriers is preferably formed by the hole barrier layer, whichmay accordingly also be formed as a confinement layer.

In one preferred configuration, the active region 6 comprises a singleor multiple quantum well structure. Structures of this type areparticularly suitable for forming an active region having a highinternal quantum efficiency.

In the context of the application, the designation “quantum wellstructure” encompasses any structure in which charge carriers experiencequantization of their energy states as a result of confinement. Inparticular, the designation quantum well structure comprises noindication regarding the dimensionality of the quantization. Ittherefore encompasses, inter alia, quantum wells, quantum wires andquantum dots and any combination of these structures.

A potential barrier for the holes, which impedes the penetration ofholes into the n-conducting region, is preferably formed by means of thehole barrier layer 7. The probability of a nonradiative recombination ofelectrons and holes outside the active region in the n-conducting regioncan be reduced in this way. The internal quantum efficiency of thesemiconductor chip can thereby be stabilized even at high currentdensities. If the hole barrier layer were dispensed with, theprobability that holes passed to the active region via the p-conductingregion would penetrate into the n-conducting region 4 would increasewith increasing current density. The internal quantum efficiency wouldthen be correspondingly reduced.

On account of the hole barrier layer 7 integrated in the semiconductorbody 3, therefore, the potential barrier that is to be overcome by holesfor entry into the n-conducting region 4 is preferably increasedrelative to a semiconductor body without a hole barrier layer.

The barrier height can be influenced by means of the band gap of thehole barrier layer 7 and/or by suitable doping of the hole barrierlayer. The band gap, by way of example, can be set by means of thealuminum content x of the hole barrier layer, the band gap alsoincreasing as the aluminum content increases. An aluminum content x of0.2 or more is particularly suitable for a hole barrier layer 7.

In order to counteract tensile strains which arise on account of thedecreasing lattice constant of the hole barrier layer as the aluminumcontent increases and which, particularly in the case of a hole barrierlayer where y=0, would occur to an increased extent as the aluminumcontent increases, in the active region 6 based for example onIn_(y)Ga_(1-y)N where 0<y≦1, the indium content y of the hole barrierlayer 7 is preferably chosen to be greater than 0. If the hole barrierlayer 7 contains both indium and aluminum and, if appropriate, gallium,then y<x preferably holds true. For matching of the lattice constant orcompensation of the strain induced by the aluminum, an indium proportiony which is less than the aluminum proportion x is particularly suitable,in particular for an active region based on In_(y)Ga_(1-y)N. The holebarrier layer may accordingly simultaneously be embodied as a bufferlayer for the active region 6 and as a barrier layer for holes.Furthermore, in particular for an indium-free hole barrier layer, thealuminum content is preferably less than or equal to 0.45. Strain can bekept small in this way.

In a preferred configuration, the hole barrier layer 7 is embodied as atunnel barrier layer. One example of a band diagram for a tunnel barrierlayer is illustrated schematically in FIG. 2. FIG. 2 schematically showsthe profile of the conduction band edge 8 and the valence band edge 9 inthe semiconductor body 3 of the semiconductor chip, which is preferablyoperated in the forward direction.

In energetic terms, the conduction band edge 78 of the hole barrierlayer 7 formed as a tunnel barrier layer lies above the conduction bandedge 48 of the layer adjoining the hole barrier layer 7 in then-conducting region 4. In energetic terms, the valence band edge 79 ofthe tunnel barrier layer lies below the valence band edge 69 of theactive region and preferably below the valence band edge 59 of the layeradjoining the active region 6 on the part of the p-conducting region 5.Electrons which are passed to the active region 6 from the n-conductingregion 4 have to overcome a potential barrier in the same way as holesfor penetration into the n-conducting region. The height of thepotential barrier to be overcome for electrons is given by thedifference between the energies of the conduction band edge 78 and theconduction band edge 48, and the height of the potential barrier for theholes is given by the difference between the energies of the valenceband edge 69 and the valence band edge 79.

The tunneling probability with which the charge carriers tunnel throughthe tunnel barrier layer depends on the respective barrier height to beovercome and the thickness of the tunnel barrier layer. To anapproximation (to a WKB approximation), the tunneling probability T isproportional to

$T \propto {\exp\left( {{- \frac{2\; d}{\hslash}}{\cdot \sqrt{{2\; m}\left( {V_{0} - E} \right)}}} \right)}$

with the absolute barrier height V₀, the barrier thickness d, and theenergy E of the charge carriers and the effective mass m of therespective charge carriers. The barrier height to be overcome by thecharge carriers is determined by the difference between the absolutebarrier height V₀—the energy of the conduction or valence band edge ofthe tunnel barrier layer—and the energy E of the respective chargecarriers. The barrier height can be set by way of the band gap, i.e.,the difference between the energies of the valence band edge and theconduction band edge of the hole barrier layer 7. As already explainedabove, this may be done by means of the aluminum content x.

FIG. 3 illustrates the tunneling probability 10 for electrons and thetunneling probability 11 for holes as a function of the thickness d ofthe tunnel barrier layer in nanometers for an Al_(0.5)Ga_(0.5)N tunnelbarrier layer in one diagram. The tunneling probabilities weredetermined on the basis of the relationship specified above. Since theeffective mass of the holes is greater than that of the electrons, thetunneling probability 11, as the thickness of the tunnel barrier layerincreases, decreases to a significantly greater extent than that of theelectrons. The effective mass of the holes amounts to approximately tentimes or more the effective mass of the electrons. This results indifferent tunneling probabilities for electrons and for holes, so that,by means of charge carrier asymmetric tunneling, a much greaterproportion of electrons than holes can tunnel through the tunnel barrierlayer. Holes are mostly kept at the active region 6 by means of thetunnel barrier layer.

The tunneling probability of the electrons through the tunnel barrierlayer may amount to ten times or more, preferably a hundred times ormore, particularly preferably a thousand times or more, the tunnelingprobability of the holes through the tunnel barrier layer. This may beachieved by forming the tunnel barrier layer in a suitable manner.

The thickness of the tunnel barrier layer is preferably 8 nm or less,particularly preferably 4 nm or less. A thickness of greater than orequal to 1 nm has been found to be particularly advantageous.Particularly suitable values for the aluminum content x are between 0.2and 0.45 inclusive in each case, preferably greater than or equal to0.3. Tunnel barrier layers with an aluminum content of this type areparticularly suitable in particular with regard to a moderate latticemismatch.

The ratio of the tunneling probability of the electrons to that of theholes may, if appropriate, additionally be increased in a targetedmanner. For this purpose, the tunnel barrier layer may be doped inn-conducting fashion, by way of example. The conduction band edge 78 ofthe tunnel barrier layer is then lowered, in the same way as the valenceband edge 79 of the tunnel barrier layer. The band gap remainsessentially constant, so that the barrier height for holes is increased,while the barrier height for electrons is reduced. A dopant havingcomparatively deep donor levels, for example Si, is particularlysuitable for this purpose.

As an alternative or in addition, it is possible to incorporate defectsinto the tunnel barrier layer in a targeted manner, which assist thetunneling of the electrons relative to the hole tunneling (trap assistedtunneling) and accordingly increase the tunneling probability forelectrons relative to that of the holes. Si, for example, is suitable asa defect atom.

A targeted lowering of the potential barrier for the electrons isindicated by dashed lines in FIG. 2. The dependence of the internalquantum efficiency on the current density can advantageously be reducedby means of the tunnel barrier layer since the holes, even at highcurrent densities, recombine radiatively in the active region 6 to anincreased extent and the penetration of holes into the n-conductingregion is effectively blocked by means of the tunnel barrier layer.

In FIG. 4, band diagrams obtained from a simulation calculationillustrate the influence of the aluminum content on the barrier heightof an Al_(x)Ga_(1-x)N tunnel barrier layer where x>0. The valence andconduction band edges in a semiconductor body similar to that shown inFIG. 1 are plotted for hole barrier layers with different aluminumcontents. The W direction indicates the growth direction of thesemiconductor body, in which the individual layers for the semiconductorbody were grown successively, e.g. epitaxially on an epitaxialsubstrate.

The conduction band edge 128 and the valence band edge 129 correspond toa nitride-compound-semiconductor-based semiconductor body without analuminum-containing tunnel barrier layer. The semiconductor chip withthe semiconductor body was assumed to be operated in forward directionat 3.4 volts.

A tunnel barrier layer 7 a where x=0.15 is provided in the case of theconduction band edge 138 and the valence band edge 139. For theconduction band edge 148 and the valence band edge 149, the tunnelbarrier layer 7 b has an aluminum content of 0.3. The barrier height ofthe potential barrier of the tunnel barrier layer increases forelectrons and also for holes with the band gap of the tunnel barrierlayer that increases on account of the increasing aluminum content. Thearrow 12 symbolizes tunneling of the electrons into the active region.

In a further preferred configuration, the hole barrier layer 7 isembodied as a pure hole barrier layer. In the case of a pure holebarrier layer, in contrast to a tunnel barrier layer, electrons passinto the active region 6 from the n-conducting region 4 essentiallyunimpeded, i.e. in a manner free of a potential barrier.

FIG. 5 schematically shows a band diagram for a pure hole barrier layer.FIG. 5 essentially corresponds to the diagram shown in FIG. 2. Incontrast thereto, the hole barrier layer 7 has a conduction band edge 78whose energy is less than or equal to that of the conduction band edge48 of a layer adjoining the pure hole barrier layer 7 on the part of then-conducting region 4. The valence band edge 79 of the pure hole barrierlayer is situated at a deeper level in energetic terms than the valenceband edge 69 of the adjoining layer on the part of the active region andpreferably at a deeper level in energetic terms than the valence bandedge 59 of a layer adjoining the active region 6 on the part of thep-conducting region 5. Electrons in the semiconductor body can thusenter into the active region 6 from the n-conducting region 4essentially in a manner free of a potential barrier, while the potentialbarrier has to be overcome by the holes in order to pass into then-conducting region 4. In contrast to a tunnel barrier layer, the purehole barrier layer may be made comparatively thick sincetunneling-through of electrons does not have to be taken into account.The probability of passage of holes into the n-conducting region can bekept extremely low in this way, for example less than or equal to 10⁻⁴or less than or equal to 10⁻⁵. By way of example, the pure hole barrierlayer has an aluminum content of between 0.2 and 0.3 inclusive in eachcase. A thickness of the pure hole barrier layer may be between 11 nmand 30 nm inclusive in each case. If appropriate, the pure hole barrierlayer may also be made thicker. Furthermore, the pure hole barrier layeris preferably doped more heavily (n⁺) than a layer which is arranged onthe part of the n-conducting region and, in particular, adjoins the holebarrier layer. The formation of a junction to the active region which isbarrier-free for electrons can be facilitated in this way. Furthermore,the conduction band edge 78 of the hole barrier layer may also lie belowthe conduction band edge 48 in energetic terms. This is indicated bydashed lines in FIG. 5.

Overall, the dependence of the internal quantum efficiency of thesemiconductor chip 1 on the current density can be reduced in asimplified manner with the hole barrier layers described above—a purehole barrier layer or a tunnel barrier layer.

This is illustrated by the diagram in FIG. 6, which shows the results ofa simulation. FIG. 6 shows the dependence of the internal quantumefficiency Q in percent of the semiconductor chip 1 on the operatingcurrent density j in amperes per square centimeter. The current densityj is plotted in logarithmic scale. The curve 14 was determined for asemiconductor chip with a semiconductor body based on a nitride compoundsemiconductor without an aluminum-containing hole barrier layer, and thecurve 13 was determined for a corresponding semiconductor body with analuminum-containing hole barrier layer. The dependence of the internalquantum efficiency Q on the current density j is greatly reduced in thecase of the curve 13 relative to the curve 14. For the semiconductorchip with the hole barrier layer, the internal quantum efficiency isessentially constant and independent of the operating current density.

FIG. 7 shows a schematic sectional view of a second exemplary embodimentof a semiconductor chip 1 according to the invention.

The semiconductor chip 1 essentially corresponds to the semiconductorchip described in connection with FIG. 1. In contrast thereto, thesemiconductor chip 1 shown in FIG. 7 is embodied as a thin-film chip.Accordingly, the carrier 2 is different from an epitaxial substrate onwhich a semiconductor layer sequence for the semiconductor body 3 isgrown epitaxially. The semiconductor body 3 may be produced on theepitaxial substrate and subsequently be arranged and preferably fixed onthe carrier 2 by its side remote from the epitaxial substrate.Advantageously, the carrier 2 does not have to satisfy the stringentrequirements made of an epitaxial substrate. The epitaxial substrate maysubsequently be removed, so that the thin-film chip is free of anepitaxial substrate. By way of example, etching, water jet cutting or alaser separating method is suitable for this purpose. For asemiconductor body based on a nitride compound semiconductor, SiC orsapphire is suitable as material for the epitaxial substrate, forexample. If appropriate, the carrier may also contain materials of thistype. As an alternative, the carrier may be metallic or embodied asceramic. This enables the electrical conductivity or the thermalconductivity to be further improved relative to an epitaxial substrate.

A metallic mirror layer 15 is preferably arranged between the carrier 2and the semiconductor body 3. Said mirror layer may prevent absorptionof radiation generated in the active region 6 in a possibly absorbentcarrier by means of reflection of the radiation at the mirror layer.Furthermore, the proportion of radiation emerging from the semiconductorbody 3 via the main area 16 remote from the carrier can be increased onaccount of the mirror layer. A connecting layer 17, by means of whichthe semiconductor body 3 is fixed on the carrier 2, is preferablyarranged between the mirror layer 15 and the carrier 2. The connectinglayer 17 may be embodied for example as a solder layer or a layer formedin a wafer bonding method. The connecting layer 17, the mirror layer 15and/or the carrier 2 is preferably embodied in electrically conductivefashion. The connecting layer 17, the mirror layer 15 and/or the carrier2 is particularly preferably electrically conductively connected to theactive region 6. The active region 6 can thus be electricallyconductively connected by means of a contact layer (not illustrated)arranged on that side of the carrier which is remote from thesemiconductor body. A corresponding counter-contact layer (notillustrated) may be arranged on the main area 16. Said contact layer(s)is(are) preferably embodied in metallic fashion.

For an active region based on nitride compound semiconductors that areparticularly suitable for generating radiation from the ultraviolet tothe green spectral range, the mirror layer 15 preferably contains Al,Ag, Pt or an alloy with at least one of said materials. Said materialsmay have advantageously high reflectivities in the aforementionedspectral ranges.

In the case of the thin-film chip, the hole barrier layer 7 is arrangedon that side of the active region 6 which is remote from the carrier 2since the semiconductor body was arranged with the p-conducting region 5on the carrier 2 after conclusion of the growth. The hole barrier layermay be formed according to the explanations above, in which case, theefficiency, in particular the coupling-out efficiency, of thesemiconductor chip can advantageously be increased on account of themirror layer and the comparatively free choice of carrier.

The scope of protection of the invention is not limited to the examplesgiven hereinabove. The invention is embodied in each novelcharacteristic and each combination of characteristics, whichparticularly includes every combination of any features which are statedin the claims, even if this feature or this combination of features isnot explicitly stated in the claims or in the examples.

In particular a hole barrier layer according to the invention can beused not only in the case of LED chips but also in the case of laserchips with an optical resonator, such as an edge-emitting laser chip, aVCSEL (Vertical Cavity Surface Emitting Laser) with an internalresonator, a VECSEL (Vertical External Cavity Surface Emitting Laser)with an external resonator or an RCLED (Resonant Cavity Light EmittingDiode).

1. A radiation-emitting semiconductor chip having a semiconductor body,wherein the semiconductor body comprises: an n-conducting region; ap-conducting region; an active region configured to generate radiationand being arranged between the n-conducting region and the p-conductingregion, electrons which are passed into the active region via then-conducting region and holes which are passed into the active regionvia the p-conducting region being recombined in the active region withthe generated radiation; and a hole barrier layer arranged on anopposite side of the active region from the p-conducting region, saidhole barrier layer containing a material from the III-V semiconductormaterial system In_(y)Ga_(1-x-y)Al_(x)N, where 0≦x≦1, x+y≦1, and y<x,the hole barrier layer being transmissive for the electrons.
 2. Thesemiconductor chip as claimed in claim 1, wherein the hole barrier layeris arranged between the n-conducting region and the active region or thehole barrier layer is integrated in the n-conducting region on a side ofthe n-conducting region that faces the active region.
 3. Thesemiconductor chip as claimed in claim 1, wherein the hole barrier layeradjoins the active region or the hole barrier layer delimits the activeregion.
 4. The semiconductor chip as claimed in claim 1, wherein x>0. 5.The semiconductor chip as claimed in claim 4, wherein x≧0.2.
 6. Thesemiconductor chip as claimed in claim 4, wherein x≦0.45.
 7. Thesemiconductor chip as claimed in claim 1, wherein y=0. 8.-9. (canceled)10. The semiconductor chip as claimed in claim 1, wherein the holebarrier layer is formed as a buffer layer, in particular for the activeregion.
 11. The semiconductor chip as claimed in claim 1, wherein theactive region is based on the material system In_(y)Ga_(1-y)N where0<y≦1.
 12. The semiconductor chip as claimed in claim 1, wherein thehole barrier layer comprises a tunnel barrier layer which is configuredsuch that electrons have a higher probability of tunneling through thetunnel barrier layer than holes.
 13. The semiconductor chip as claimedin claim 25, wherein the tunnel barrier layer has a thickness of 8 nm orless.
 14. The semiconductor chip as claimed in claim 12, wherein thetunnel barrier layer is doped in an n-conducting manner or is embodiedintrinsically.
 15. The semiconductor chip as claimed in claim 1, whereinthe hole barrier layer comprises a pure hole barrier layer which blocksholes from passing through.
 16. The semiconductor chip as claimed inclaim 30, wherein the pure hole barrier layer is completely transmissivefor the electrons.
 17. The semiconductor chip as claimed in claim 30,wherein the pure hole barrier layer is doped in an n-conducting mannersuch that energy of a conduction band edge of the hole barrier layer isless than or equal to the energy of the conduction band edge of a layeradjoining the hole barrier layer on a side of the hole barrier layerwhich is opposite to the active region.
 18. The semiconductor chip asclaimed in claim 30, wherein the pure hole barrier layer has a thicknessof 11 nm or more.
 19. The semiconductor chip as claimed in claim 1,wherein the semiconductor chip comprises a thin-film chip.
 20. Thesemiconductor chip as claimed in claim 1, wherein the semiconductor bodyis arranged on a carrier.
 21. The semiconductor chip as claimed in claim20, further comprising a mirror layer arranged between the active regionand the carrier.
 22. The semiconductor chip as claimed in claim 21,wherein said mirror layer is metallic.
 23. The semiconductor chip asclaimed in claim 25, wherein the tunnel barrier layer has a thickness of4 nm or less.
 24. The semiconductor chip as claimed in claim 15, whereinthe pure hole barrier layer completely blocks holes from passingthrough.
 25. A radiation-emitting semiconductor chip having asemiconductor body, wherein the semiconductor body comprises: ann-conducting region; a p-conducting region; an active region configuredto generate radiation and being arranged between the n-conducting regionand the p-conducting region, electrons which are passed into the activeregion via the n-conducting region and holes which are passed into theactive region via the p-conducting region being recombined in the activeregion with the generated radiation; and a hole barrier layer arrangedon an opposite side of the active region from the p-conducting region,said hole barrier layer containing a material from the III-Vsemiconductor material system In_(y)Ga_(1-x-y)Al_(x)N where 0≦x≦1,0≦y≦1, and x+y≦1, the hole barrier layer being transmissive for theelectrons; wherein the hole barrier layer comprises a tunnel barrierlayer which is configured such that electrons have a higher probabilityof tunneling through the tunnel barrier layer than holes, and whereinthe tunnel barrier layer is doped in an n-conducting manner or isembodied intrinsically.
 26. The semiconductor chip as claimed in claim25, wherein the semiconductor chip comprises a thin-film chip.
 27. Thesemiconductor chip as claimed in claim 25, wherein the semiconductorbody is arranged on a carrier.
 28. The semiconductor chip as claimed inclaim 27, further comprising a mirror layer arranged between the activeregion and the carrier.
 29. The semiconductor chip as claimed in claim28, wherein said mirror layer is metallic.
 30. A radiation-emittingsemiconductor chip having a semiconductor body, wherein thesemiconductor body comprises: an n-conducting region; a p-conductingregion; an active region configured to generate radiation and beingarranged between the n-conducting region and the p-conducting region,electrons which are passed into the active region via the n-conductingregion and holes which are passed into the active region via thep-conducting region being recombined in the active region with thegenerated radiation; and a pure hole barrier layer arranged on anopposite side of the active region from the p-conducting region, saidpure hole barrier layer blocking holes from passing through andcontaining a material from the III-V semiconductor material systemIn_(y)Ga_(1-x-y)Al_(x)N, where 0≦y≦1, 0≦y≦1, and x+y≦1, the pure holebarrier layer being transmissive for the electrons.
 31. Thesemiconductor chip as claimed in claim 30, wherein the semiconductorchip comprises a thin-film chip.
 32. The semiconductor chip as claimedin claim 30, wherein the semiconductor body is arranged on a carrier.33. The semiconductor chip as claimed in claim 32, further comprising amirror layer arranged between the active region and the carrier.
 34. Thesemiconductor chip as claimed in claim 33, wherein said mirror layer ismetallic.